Branching unit for submarine systems

Abstract

A branching unit for use in submarine telecommunications optical cable systems which employs electrical power feeding for repeater/regenerators of the cable system, in particular a system employing multiple branching units. The unit terminates three line cables (at 1, 2, 3) and a sea earth (at 4) and includes first, second the third high voltage relays (A, A1, B, B1, C, C1), only one of which is energized at a time. When electrical power is supplied between any two line terminations, e.g. 1 and 3, an associated relay coil, e.g. C is energized so that its contacts C1 isolate the third line termination, e.g. 2, and connect it to the sea earth termination (4) via fourth, or fifth, relay contacts (D1, E1 ). The branching unit also includes a plurality of optical regenerators, for optical path switching purposes, which require electrical power feeding and whose power feed circuits 20 are connected in parallel with each of the relay coils. When any relay is energized, i.e. the cable system is powered up, the regenerators are also powered. The zener diodes (21) provide voltage supply to the regenerator power feed circuits as well as providing surge protection for them and the relay coils simultaneously. The fourth-and fifth relays (D, D1, E, E1) serve to prevent arc transfer in the first, second and third relays (FIG. 4).

I claim: 
     
       1. A branching unit for use in submarine telecommunications optical cable systems employing electrical power feeding, the unit having a respective termination for each of three line cables and a termination for a sea earth, a plurality of optical regenerators requiring electrical power feeding and including a plurality of power feed circuits connected in series with one another, first, second and third electrical relays connected to said power feed circuits and only one of said relays being energisable at a time, and a fourth electrical relay connected to said first, second and third electrical relays, and said electrical relays being connected such that when electrical power is supplied between any pair of line cable terminations the third line cable termination is coupled to the sea earth via the fourth relay which is powered by said electrical power to thereby isolate the third line cable termination from said pair of line cable terminations, and the plurality of power feed circuits of the optical regenerators are disposed in series between said pair of line cable terminations to achieve power feeding of the optical regenerators. 
     
     
       2. A branching unit as claimed in claim 1 wherein the first, second and third relays have relay coils, said coils being arranged in a delta network with each coil being connectable between a respective pair of the line cable terminations via rectifier diodes, and wherein relay contacts corresponding to each coil of a said pair of line cable terminations are associated with the third line cable termination and the sea earth termination, such that power application between a said pair of line cable terminations causes switching of relay contacts of the coils of the relays of said pair of line cable terminations and said fourth relay such that the third line cable termination is connected to the sea earth termination. 
     
     
       3. A branching unit as claimed in claim 2 and including a zener diode arrangement comprising a plurality of zener diodes connected in series, each relay coil being disposed in parallel with the zener diode arrangement, and each zener diode of the arrangement being disposed in parallel with a respective one of said optical regenerator power feed circuits. 
     
     
       4. A branching unit as claimed in claim 3 and including three pairs of series connected rectifier diodes, each pair being associated with a respective line cable termination, disposed in parallel with the series connected zener diodes and the series connected optical regenerator power feed circuits, wherein each line cable termination is connectable to a point between the two rectifier diodes of the respective pair, each coil being connected across a respective pair of said points, the four rectifier diodes associated with a said coil being arranged as a rectifier bridge, and wherein the zener diodes provide surge protection for the regenerators, the relay coils and the rectifier diodes simultaneously. 
     
     
       5. A branching unit as claimed in claim 4, wherein between each line cable termination and the respective point is disposed a respective surge protection coil. 
     
     
       6. A branching unit as claimed in claim 5, wherein the relay coils of the first, second and third relays each have associated therewith a respective rectifier bridge whereby to prevent the line current reversals unlatching an actuated relay and causing surges at the relay contacts. 
     
     
       7. A branching unit as claimed in claim 1, wherein the fourth relay has a relay coil arranged in series with a parallel connection of first contacts of the first, second and third relays and which relay coil and first contacts are arranged in parallel with the plurality of power feed circuits, and wherein second contacts of the first, second and third relays are associated each with a respective one of the line terminations and relay contacts of the fourth relay are associated with the sea earth. 
     
     
       8. A branching unit for use in submarine telecommunications optical cable systems employing electrical power feeding, the unit having a respective termination for each of three line cables and a termination for a sea earth, a plurality of optical regenerators requiring electrical power feeding and including a plurality of power feed circuits connected in series with one another, first, second and third electrical relays connected to said power feed circuits and only one of said relays being energisable at a time, and fourth and fifth electrical relays connected to said first, second and third electrical relays, the fourth and fifth relays having relay coils arranged in series and the series arranged relay coils being PG,20 arranged in parallel with the plurality of power feed circuits, and including means for operating the fourth relay if current flow is in one direction between a pair of said terminations and for operating the fifth relay if current flow is in an opposite direction to said one direction between said pair of terminations, and including means such that when electrical power is supplied between any pair of line cable terminations the third line cable termination coupled to the sea earth via the fourth relay which is powered by said electrical power to thereby isolate the third line cable termination from said pair of line cable terminations, and the plurality of power feed circuits of the optical regenerators are disposed in series between said pair of line cable terminations to achieve power feeding of the optical regenerators.